Joint design welding dissimilar materials

ABSTRACT

A joint site design for welding of a shaft has a tubular shape composed of a hard material with a hub having a flat shape composed of softer material. The shaft is joined by welding at a connection area located at an end face thereof to a connection area of the hub located at a radial shoulder thereof.

TECHNICAL FIELD

The invention relates to a joint site design for friction welding of a shaft of a hard material with a hub consisting of softer material.

BACKGROUND

In vehicle construction, composite workpieces which are composed of a shaft and an essentially rotationally symmetrical hub part are used in numerous applications. Examples of hubs are transmission and clutch parts or also disk-shaped blanks which are still to be mechanically processed.

It is known to join a shaft and hub part in a connection region by friction welding. In this case, an end face of the shaft is joined to an end face of the hub part in a conventional manner. Alternatively, the shaft and hub part can be joined by means of overlap friction welding; this involves a variant of pressure welding in which, in contrast to conventional end-face friction welding, the surfaces to be joined are arranged at the circumference of the components. In this case, for example, a shaft is welded to a hub part with overlap by one of the two components being set in rotation and being pressed onto the other stationary counterpart. The welding process starts at the contact surfaces of the components. After the plasticization of the material located there by the friction heat, a permanent joint is obtained after the end of the rotary movement.

Shown in DE 199 34 855 C1 is a friction-welded shaft/disk composite workpiece which is assembled from a disk having a through-hole and from a shaft by means of overlap friction welding. During the welding of shaft and disk, annular connection sections are produced, between which annular cavities are formed. A reduction in the weight of the entire part is achieved by the joint sites offset from one another radially and axially, it being possible for the cavities to be used, for example, for directing oil.

In the state of the art shafts and hubs for a composite clutch are connected by a intermeshing toothing between the components to achieve a frictional or positive fitting connection. The use of the clutches is mainly in transfer cases and automatic transmission applications.

Known applications have a so called “tube to tube” joint design. This means that friction welding takes place between two end faces which have a pipe shape. In comparison to the pipe shaped end face of the softer part the harder part has a larger or equal pipe outside diameter and a smaller or equal pipe inside diameter. With other words the harder part has an equal or larger end face than the soft part. This guarantees that the end face of the softer part will always fully touch the end face of the harder part. The harder side keeps being pipe shaped in the joining location, but the softer part has a flat surface in the joining location. This means that the softer part has the larger joining surface (“end face”). This has major advantages in terms of packaging and cost. The end face of the harder part is designed in a way that it is guaranteed that the typical material squeezing out can take place in order to create an atomic bond.

SUMMARY

An object of the invention is to specify a novel design of the joint site for a shaft-hub composite workpiece for a clutch, with which design the mechanical strength properties of the joint are increased.

Another object is to find a joint design for friction welding of a harder material (higher melting point) with a softer material (lower melting point) with the challenge of having a simple and cheap part preparation and with the target of meeting lowest package specifications.

These objects are achieved in accordance with the invention by the features of independent claim. Advantageous configurations can be gathered from the subclaims.

In accordance with the invention the joint design for friction welding of a harder with a significant softer material comprises a tubular shape on the harder and a flat shape on the softer side. This means the joint design is adapted to weld a material with a higher melting temperature with a material with significant lower melting temperature, where the side with higher melting temperature has a tubular shape and the side with lower melting temperature has a flat shape.

In accordance with the invention, the joint-site structure of a shaft-hub composite work piece, in particular for joining a shaft to a connection area of a hub part of a clutch by means of friction welding, is designed in such a way that connection area of a hub part is located a defined distance apart the inner circumference of the hub part and the spread of the material softened during the friction welding is not flowing up to the edge of the hub part component.

The advantages provided in accordance with the invention is a reduction in manufacturing costs for the softer part. The variation of the friction welding shortening decreases significantly. The solution in accordance with the invention reduces package space compared to state of the art friction welding joints. The invention allows the usage of low weighted materials for clutches replacing actual common designs.

To reduce weight of a vehicle all part has to be as light as constructional possible and the inventional solution opens a way to design a clutch with low weight material.

The projection or protrusion on account of the forced-out material at the joint site is preferably machined after the friction welding in order to obtain a rounded portion.

In an advantageous configuration of the invention, a plurality of joint sites axially offset from one another are provided between shaft and hub part. In this case, it is advantageous for the self-centering and relative axial orientation of the joining members during the friction welding to offset the joint sites of the joining members axially and radially relative to one another in such a way that the joint sites of the joining members on the composite workpiece, after the welding, are arranged at an angle of between 10° to 20°, preferably 15°, to one another. The composite workpiece produced is then cylindrically symmetric.

This end-face friction welding of the shaft to the hub part avoids conical distortion of the hub part occurring due to asymmetrical shrinkage of the hub part after the friction welding. The method in accordance with the invention is not associated with any conical distortion of the joining members at all; the original cylindrical symmetry of the two joining members is thus retained in the composite workpiece with high accuracy.

The shaft and hub part may be made of different materials. In particular, a hardened shaft may be used, and/or the hub part may be finish-machined (hardened, ground, etc.).

DRAWINGS

Embodiments of the invention is described below with reference to an exemplary embodiment shown in the schematic drawings. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and form appropriate further combinations therefrom.

FIG. 1 illustrates a shaft hub composite work piece.

FIGS. 2 a to 2 d illustrate the structure of a joint site.

DESCRIPTION

In accordance with FIG. 1, a shaft 2, e.g., an input shaft of a clutch for a motor vehicle, is joined to a hub part 1 of a clutch having a connection area 4 with a substantially flat or planar surface/cross-section. The joining or connection area 4 is formed at the surface of a radial shoulder 8 of the hub that forms a rim with a 90° angle between hub and shoulder. The radial shoulder 8 must have a dimension that allows the shaft 2 to contact the end faces 5 to a flat area of the radial shoulder 8.

At the shaft 2 the joining area 3 having a substantially tubular shape/cross-section is finally in direct contact with connection area 4 of the hub part 1. The end face 5 of the shaft 2 is illustrated in detail in FIGS. 2 a, 2 b, 2 c and 2 d. The end face 5 as illustrated in FIG. 2 a is a flat end face. The position of the end face 5 in relation to the hub 1 and the inner opening circumference 6 is illustrated in this figure. The shaft end face 5 is placed a predetermined distance d1 away from inner circumference 6. The shaft 2 material can be composed of steel and the hub 1 can be composed of a metal such as aluminium or another low weight metal or alloy.

Due to the friction welding, the heated, soft material escapes from the joining area 3 and forms a projection 7 of material around the end face 5 of the shaft 2. The joining area 3 is allocated in a way to avoid that the melted material flow to the edge of the hub 1. The predetermined distance d2 between the inner circumference 6 and the end position of the melted material is at least 1 mm to maintain dimension and structure of the hub 1. So the joining area 3 is allocated so that d1>d2 is realized, wherein d2 is approximately between 1 to 5 mm.

The projection or protrusion 7 of the material of the joint site is obtained after the friction welding, and this projection or protrusion 7 can be machined, for example, after the friction welding in order to obtain a rounded portion 7.

The face end 5 of the shaft can be optimized or the welding process and the joint.

Alternative solutions are illustrated in the FIGS. 2. FIG. 2 a illustrates a flat end face parallel to the flat area 4 of the hub and perpendicular to the long axis of the shaft. FIGS. 2 b and 2 d illustrate inclined faces 5 that result in asymmetric joints. The solution of FIG. 2 c illustrates a curved or convex end face of the shaft 2.

To produce a composite work piece of a shaft 2 for a clutch having a connection area 4 of a hub part, first of all a one-piece hub unit-comprising the hub part and the connection area-is produced. Then hub and shaft are connected by friction welding.

Although embodiments have been described herein, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 

What is claimed is:
 1. A joint site comprising: a shaft having a first body with a tubular shape and being composed of a first material having a first hardness; a hub having a second body with a flat shape and being composed of a second material having a second hardness that is less than the first hardness, wherein the shaft is configured for joint-connection at a first connection area to a second connection area of the hub by welding.
 2. The joint site of claim 1, wherein the first connection area comprises an end face of the first body.
 3. The joint site of claim 1, wherein the second connection area comprises a radial shoulder of the hub.
 4. The joint site of claim 3, wherein the second connection area is located a predetermined distance from the inner circumference of the hub.
 5. The joint site of claim 4, wherein the predetermined distance is greater than the thickness of a protrusion of melted material of the hub at the second connection area.
 6. The joint site of claim 5, wherein the protrusion is spaced a second predetermined distance and the inner circumference of the hub.
 7. The joint site of claim 6, wherein the first predetermined distance is greater than the second predetermined distance.
 8. The joint site of claim 1, wherein: the first connection area comprises an end face of the first body; and the second connection area comprises a radial shoulder of the hub.
 9. The joint site of claim 8, wherein the second connection area is located a predetermined distance from the inner circumference of the hub.
 10. The joint site of claim 9, wherein the predetermined distance is greater than the thickness of a protrusion of melted material of the hub at the second connection area.
 11. The joint site of claim 10, wherein the protrusion is spaced a second predetermined distance and the inner circumference of the hub.
 12. The joint site of claim 11, wherein the first predetermined distance is greater than the second predetermined distance.
 13. The joint site design of claim 8, wherein the surface of the end face of the shaft is flat and perpendicular to the longitudinal axis of the shaft.
 14. The joint site design of claim 8, wherein the surface of the end face of the shaft is flat and inclined relative to the longitudinal axis of the shaft.
 15. The joint site design of claim 8, wherein the end face of the shaft has a conical cross-section.
 16. The joint site design of claim 1, wherein joint sites of joining members on a composite workpiece, after the welding, are arranged at an angle of between 10° to 20° to one another.
 17. The joint site design of claim 1, wherein joint sites of the joining members on the composite workpiece, after the welding, are arranged at an angle of 15° to one another.
 18. The joint site design of claim 1, wherein the hub and the shaft are components of a clutch.
 19. The joint site design of claim 1, wherein the joint site is configured for use in a transfer environment and automatic transmissions.
 20. A joint site comprising: a first body having an end face, the first body comprising a first material having a first hardness; a second body having a radial shoulder, the second body comprising a second material having a second hardness that is less than the first hardness, wherein the first body is configured for joint-connection at the end face to radial shoulder of the second body by friction welding. 